# L6203 motor driver with high Rds(on)

The L6203 states that it typically has and Rds(on) of about 0.3 ohm. After implementing the circuit below, I'm measuring a significant voltage drop across the transistors when the motor is stalled (or with increased current). The results correspond to a Rds(on) between 1.5 and 2 ohm. I'm using a supply voltage of 17 V.

This is much greater than the value indicated on the front page of the datasheet of 0.3 ohm. Furthermore, the device is labelled on the datasheet as being "High Efficiency". The only conclusion that I can make is that I may be missing something important. My problem/results are very similar to a previous post which was never fully resolved. I'm hoping someone could offer some new insight?

Edit

Here is some more data. The circuit is as shown above with a 1uF capacitor between Vs and gnd.

• Load is a 5 ohm motor at stall
• Supply voltage (after series multimeter measuring supply current) = 15.8V
• EN = high
• V_IN1 = 5V PWM at 80% duty
• V_IN2 = gnd
• Total current draw from supply = 1.6A
• V_OUT1 = 1.8V
• V_OUT2 = 9.6V
• The chip is at room temperature for these measurements

If the load is removed then output waveform swings to the rails as expected. These results seem to indicate a much larger Rds(on) than 0.3 ohm as stated by the datasheet.

• What current is the motor taking? May 8, 2019 at 14:04
• Supply voltage is 17V, motor resistance is 5 ohm. I'm struggling to get anything over 2A. That is without switching, just operating with one input high and the other low. May 8, 2019 at 14:09
• How are you powering your circuit? Because if you go to page 5 of the datasheet, and see the Vs/Rdson curve, they show the correlation between Rdson and the supply voltage Vs. If the stalled motor is consuming too much current, it might be that the voltage of your power supply is dropping, increasing significantly the Rdson May 8, 2019 at 14:09
• I'm afraid it's not the supply. 2-5A is no problem for my supply :) May 8, 2019 at 14:11
• I can't find it in the the datasheet at the moment, but a lot of drivers that have a high-side charge pump won't work right if you hold the high-side on solid -- there's some minimum off period and maximum on period that you have to observe, or the high-side gate won't be held above the supply voltage. You might want to dig through the datasheet, or do the experiment of driving the thing with just a bit of PWM and see if that helps. May 8, 2019 at 15:13